It is the usual practice in modern hospitals to perform a variety of chemical and other tests on whole blood samples obtained from the patients. One important test is to determine the glucose content in the whole blood sample. However, due to glycolysis, the whole blood sample rapidly loses its glucose content under normal ambient conditions, unless some preservative is included in the sample to prevent glycolysis. However, it is important that the preservative does not produce any significant hemolysis in the sample which would tend to destroy its effectiveness. Also, it is important that the preservative does not affect other blood constituents so as to interfere with the results of other tests that are to be performed on the blood sample.
Sodium fluoride has been extensively used in the past as a preservative for glucose in blood samples. Sodium fluoride does prevent glycolysis, but it is known to interfere with certain enzyme reactions, such as urease. Also, glucose results have been found to be affected by sodium fluoride when certain oxidaseperoxidase techniques are employed.
Sodium iodoacetate has also been used in the past to prevent the loss of glucose in blood samples (see, for example, Principles of Biochemistry, 4th Edition, McGraw-Hill (1968) Pages 238, 239 and 398, 399). This latter preservative is preferable to sodium fluoride since it has the advantage of not interfering with the urease reaction when determining urea nitrogen. However, both the sodium fluoride and sodium iodoacetate preservatives have a disadvantage in that they produce excessive hemolysis in the blood sample.
The principal objective of the present invention is to provide preservatives for preventing glycolysis in the blood samples, which have all the advantages of sodium iodoacetate in that they do not interfere in any way with any of the other known blood constituents, and which have the additional advantage over sodium iodoacetate that they do not produce any significant hemolysis in the blood samples or add sodium to the sample.
The preservatives of the present invention have been found to stabilize glucose in a blood sample for at least twenty-four hours when standing on the clot at room temperature. The preservatives constituting the preferred embodiments of the invention are Tris-Iodoacetate; either Sodium or Tris Bromoacetate, or salts of mono Chloroacetic acid. The Tris-Iodoacetate preservative at 0.4 mg/ml of blood has been found to produce four and one-half times less hemolysis than fluoride. The Sodium Bromoacetate at 1 mg/ml of blood has been found to produce no hemolysis. Chloroacetic acid salts have been found to exhibit the same glycolytic properties as the Iodo and Bromo Acetic acid salts. Other salts of Iodoacetic acid, such as ammonium and other amines, are also effective for the purpose.